The research objectives include 'analytical' and 'synthetic aspects'. A variety of techniques including recording from individual sensory and motor control neurons and muscles, the making of permanent lesions and reversible blocks by cooling of subcortical nuclei, will be used to identify the neural components and their interrelationships subserving contact placing. Special emphasis will be placed on weighing the role of sensory input during contact placing as compared with ballistic components. The patterns of activity as selected points in the higher sensorimotor control circuit will be compared when movements are initiated by a) contactual stimulation (e.g. contact placing and the play-attack reflex) and b) non-contactual stimulation (e.g. visual placing and 'Searching' movements of an unsupported similar set of muscles but with different temporal relationships to one another, are represented by different patterns of discharge at key points in the higher motor control system. The development of contact placing and of the associated neural circuits will be studied with particular reference to the location of the subcortical circuit which can manage contact placing during the precritical period. A hypothesis to be tested is that the development of functioning by sensorimotor cortex overlaps that of the subcortical circuit, which subsequently loses its 'stand alone' capacity. Contact placing and its associated neural circuity will be studied electrophysiologically during forms of plasticity. Special emphasis will be laid on cellular activities of VA-VL, the input from the entopeduncular N and monosynaptic inputs to the large PT neuron. The project depends on data processing by computer. Appropriately programmed CDC 160A and PDP 11/45 systems are utilized in different aspects of the project. BIBLIOGRAPHIC REFERENCES: Amassian, V.E., Reisine, H. and Wertenbaker, C. Neural pathways subserving plasticity of contact placin. J. Physiol., 1975, 242:67-69P. Amassian, V.E. and Ross, R. Short-term dependence on sensorimotor cortex of contact placing by kittens during the precritical period. J. Physiol., 1975, 246:101-103P.